Simple 3-Channel Stereo Mixer with VU Meter

Dear Readers, please welcome a new contributor Colin Merkel. His projects include an impressive built from scratch micro controller based looper and now a simple Stereo Mixer.  I’m sure this will be useful in circuit bending applications. It is worth noting that the project below was built from spare parts and could be done much smaller if needed. – CM

My name is Colin Merkel, and recently I have been annoyed by the audio setup in my room. I have some really awesome speakers, but they are usually attached to my computer-when I want to plug my iPod in, or anything else for that matter, I have to fiddle around with 3 different cables – very frustrating!

So, to fix my problem, I put together a simple 3 channel stereo mixer.

Mixer

As you can see from the photograph, there is an analog VU meter, one volume knob and mute switch per channel, and a master volume control in the form of left/right level sliders.

[youtube]http://www.youtube.com/watch?v=PbkShNxeJhg[/youtube]

The electronics behind the system are extremely simple- in fact, I used only a single LM324 quad op-amp, some resistors, and some diodes. The entire circuit runs off of a 12V DC wall wart power supply. Shown below are poorly-drawn schematics for the left and right channels.

As a possible improvement, I may add a headphone jack on the front so that you it would be easy to put all the mixer output through headphones. Here are some photos from the build:

Breadboard layout
Testing on the breadboard!
Soldering the circuit...
Completed circuit
Completed circuit
Have to keep good notes...

Anyway, the mixer was an easy build that managed to make my audio system a little bit more awesome. Thanks for reading! If you have any comments or questions, feel free to ask.

21 thoughts on “Simple 3-Channel Stereo Mixer with VU Meter”

  1. Sorry for the poorly-drawn schematics! I’m glad you were able to make use of the article.

    The bridge rectifier is used for the VU meter. Those +VU and -VU are the terminals of the VU meter (the volume needle meter).

    If you don’t need the VU meter then you can leave out all of that.

  2. quick (possibly stupid) question, would it be possible to replicate the right channel diagram multiple times to make an (x)number of channels mixer?

  3. @skgb: yes, absolutely, this can be configured to as many channels as you would want.

  4. I started to build this thing, but i was confused about the input Pot and input resistor. On the pictures i see the colorcode is Green Red Yellow(520K), so the 500K in the schematic is the resistor? If so, what Ohm are the pots? (I figured the Pots were 500K when buying).

    Could you clear this up for me?

  5. @flox yes, the resistor is 500k. The potentiometer can be anything really, 500k should be fine.

  6. i just wondering maybe someone can draw and share with us full schematic with headphone improvement instead.
    i would be thankful for rest of my life.

    and is this possible to replace RCA inputs with just stereo 6.3mm Headphone Plug?

  7. Hi nice work (simple & cheap construction) iam having some questions
    iam newbie in electronics perhaps some questions sound silly

    1: regarding the inputs L+R channels are they potensiometers(lin or log)? and then 500k resistors are followed up from left to right direction?

    2: the 1?F capacitors are ceramic or electrolyte? because in our market there are no ceramic 1?F capacitors

    3: about the LM324 pin layout which pin is connected to? and power supply also

    thanks in advance

  8. @flotsam&jetsam: 1: pots don’t really matter. lin vs. log is really just using log for audio applications. if you use a linear, it will sound like 70% of the volume is in the first 20% of the knob or so. Basically for audio the pot’s taper is so that the volume doubles for every 10% or so. (this is simplified, but is the basic idea.

    2: doesn’t really matter. typically anything 1uF and above will be electrolyte, and for this application it would be fine. Electronically cap type doesn’t matter, but some caps may have better sound than others. In this mixer you probably couldn’t notice a difference.

    3: just grab the lm324 data sheet. It is effectively 4 separate op amps in one IC. You could just well use 4 741 ops amps in it’s place, or two dual op amps like the TL072. Each op amp will have an inverting input (the minus on the lower part of the triangles in the schematic) a non-inverting input (the plus) and an output (the right point of the triangle. The benefit to the quad op-amp is that you only need one power and ground. If you aren’t using a VU meter, a TL072 would be ideal. Just make sure your chip can handle whatever voltage you are bringing into it, most can handle a range.

  9. Hi there,
    I’ve tried to replicate this circuit, but I just get a similar volume, seriously distorted sound output.
    Just wondered if anyone had any clear schematics, or thoughts on what may be causing the issue.
    Thanks in advance, Daniel.

  10. Hi there

    I realise this is an old post so I’m kinda hoping someone will provide an answer.

    I can’t seem to find a LM324 anywhere in the UK but there are loads of places selling the LM324N. Will this do?

    Thanks

    Ash

  11. Glad to see people are still reading this stuff!

    Any general purpose quad op amp will do. LM324N will work for sure.

  12. Just what I need, I have 2 computers and an iPhone and want them all connecting to my PC speakers at the same time.

    I’ve looked high & low for a small/simple 3-ch stereo mixer to no avail.

    Time to get out my soldering iron 🙂

    BTW you can get the LM324 from http://www.cpc.co.uk

  13. Great work…wat is that 4 diodes in right input circuit diagram…????? and a opamp connected to that diodes???????

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